This invention relates to invasive medical devices which aid in the catheterization of human blood vessels. In particular, this invention relates to a releasably locking dilator and tear away sheath assembly, which is used to enlarge an opening in a patient""s blood vessel during insertion of a catheter into the blood vessel and then guide the catheter into the blood vessel to be catheterized.
Catheters are used in numerous medical procedures. In particular, catheters are used for the introduction or removal of fluids from various venous regions and vessels throughout the body, such as for hemodialysis. The procedure by which these catheters are introduced to the body is delicate and complex. One particularly intricate challenge to catheterization is enlarging a hole in the flesh and vessel to be catheterized while minimizing blood loss and trauma to the patient.
Generally, to insert any catheter in a blood vessel, the vessel is identified by aspiration with a long hollow needle in accordance with the Seldinger technique. When blood enters a syringe attached to the needle, indicating that the vessel has been found, a thin guide wire is then introduced, typically through the syringe needle or other introducer device, into the interior of the vessel. The introducer device is then removed, leaving the guide wire within the vessel. The guide wire projects beyond the surface of the skin.
At this point, several options are available to a physician for catheter placement. The simplest option is to pass a catheter into the vessel directly over the guide wire. The guide wire is then removed. However, use of this technique is only possible in cases where the catheter is of a relatively small diameter, made of a stiff material and not significantly larger than the guide wire. If, however, the catheter is of a relatively large diameter and/or not made of a stiff material, one preferable method of inserting the catheter into the vessel is through an introducer sheath. The introducer sheath is simply a large, stiff thin-walled tube, which serves as a temporary conduit for the catheter that is being placed. The sheath is positioned by placing a dilator, which has a hollow passageway along its longitudinal axis, inside of the sheath and passing both the dilator and the sheath together into the vessel over the guide wire. The dilator expands the opening in the blood vessel to allow for catheter insertion into the vessel. The guide wire and dilator are then removed, leaving the thin-walled sheath in place. The catheter is then inserted through the sheath.
In a setting where a catheter with a hub or other attachment at the end of the catheter has a feature which is larger than that of the inner diameter of the sheath, it is necessary to have a tear-away sheath that can be split away from the catheter as the sheath is being removed from the patient. By splitting the sheath along its longitudinal axis as the sheath is being removed from the patient, the inserting physician will be able to pull out the sheath in such a way that the portion removed from the patient is split, thereby not interfering with any encumbrances on the catheter. Generally, tear away sheaths are manufactured in a way that aids in the tearing of the sheath at two opposing points on the circumference of the sheath, thereby splitting the sheath into two halves separated longitudinally through the center of the sheath.
A sheath is generally constructed with a hub at its proximal end. This hub serves as a handle, a mating point for a dilator, and a flat surface to aid in the prevention of blood loss or contamination. When a sheath needs to be split apart in order to be successfully withdrawn from the body while leaving the catheter in place, the hub will also have to be split apart in order to clear the catheter. Preferably, the hub will split along the same lines as the sheath. To accomplish this, the hub must be designed with reveals or other weaknesses along two longitudinal lines aligned with the weaknesses in the sheath. Some previous examples of these weaknesses are tabs or webs which connect two halves of the hub, or recesses in the material comprising the hub. The weaknesses in the hub will help the inserting physician to break apart the hub in line with the tear seams on the sheath.
Another important facet of the hub is a set of tabs that protrude from the center. These tabs not only help the inserting physician to align, insert and withdraw the sheath, but also to pull the sheath so that the sheath can be removed from around a catheter while still leaving the catheter in place. There are a number of different tab configurations, but it is important to have one which allows for easy maneuverability, control, and leverage. One design includes a hub wherein the tabs protrude from the hub perpendicular to a plane which includes the tear seams in the sheath and the longitudinal axis of the sheath. In this design, the tabs are diametrically opposed from each other and are spaced in such a way that when the tabs are grasped and pulled apart from each other, the sheath and its hub will split down the middle. Another desirable feature of the tabs is that the tabs provide leverage for breaking apart the hub in a manner that does not cause trauma to the incision in the body.
In the case where a sheath does not have a small diameter or a narrow point, the dilator is often used to aid in the insertion of the sheath. The dilator has a long tubular section, the outside diameter of which is slightly smaller than the inside diameter of the sheath. The dilator also has a pointed tip on its distal end and a hollow center, which runs along the entire length of the dilator. The dilator is inserted into the body with the guidewire running through its center, thereby allowing the tip of the dilator to follow the guidewire to the place that is to be catheterized. On its proximal end, the dilator may have a hub. Like the hub of the sheath, this hub can also serve a number of purposes, such as providing a stable handle to aid in guiding the dilator into the vein, and as a mechanism which can mate with the sheath hub to form a locked connection.
Some dilator and sheath assemblies that include a connection between the dilator and sheath are known. U.S. Pat. No. 5,885,217 to Gisselberg et al. discloses a dilator and sheath assembly, wherein the dilator and sheath are held together by locking tabs which provide a stop to hold the dilator in place during insertion. However, in this configuration, the dilator may rotate about its longitudinal axis in relation to the sheath, thereby inadvertently and prematurely disengaging the dilator from the sheath. U.S. Pat. No. 5,098,392 to Fleischhacker et al. discloses a dilator and sheath assembly, wherein the dilator is attached to the sheath through a clamp wherein the clamp is part of the dilator hub. However, this design presents the ability to come unclamped leading to the dilator backing out of the sheath. U.S. Pat. No. 4,772,266 to Groshong discloses a dilator and sheath assembly, wherein the hubs of the dilator and the sheath lock together by means of compression. However, it would be possible for the dilator to back out of the sheath in this configuration if excessive force is exerted on the tip of the dilator.
It would be beneficial to provide a dilator and sheath assembly that incorporates a stable releasably locking mechanism to prevent the dilator from backing out of the sheath longitudinally during insertion which is not prone to coming unlocked or releasing during use. Moreover, it would be beneficial for this type of mechanism to have handles, which allow the inserting physician to gain leverage in the process of splitting the sheath apart.
Briefly, the present invention provides a releasably locking dilator and sheath assembly and methods for releasing the dilator from the sheath and longitudinally splitting the sheath in the course of inserting a catheter into a desired vessel to be catheterized.
The invention provides a releasably locking dilator and sheath assembly, comprising a dilator and a sheath. The dilator has a distal tip, an elongated dilator stem, a proximal dilator end, and a dilator hub fixedly connected to the proximal dilator end. The dilator hub includes a threaded portion on its distal end. The sheath comprises a distal end, an elongated hollow tubular section, a proximal sheath end, and a sheath hub fixedly connected to the proximal sheath end. The sheath also comprises a longitudinal axis extending between the proximal sheath end and the distal sheath end as well as at least one tear seam disposed longitudinally on the sheath surface. The sheath hub includes a proximal portion and a mating threaded portion at a proximal end thereof. The threaded portion of the dilator hub and the mating threaded portion of the sheath hub provide a releasably locking engagement between the dilator and the sheath. The sheath is sized to frictionally retain the dilator.
The invention further provides a releasably locking dilator and sheath assembly, wherein the dilator comprises an elongated dilator stem having a proximal end and a dilator hub fixedly connected to the proximal dilator end. In addition, the sheath comprises an elongated tubular portion having a longitudinal axis, a proximal sheath end and a distal sheath end. The tubular portion of the sheath is sized to frictionally retain the dilator stem. The sheath also comprises at least one tear seam extending between the proximal sheath end and the distal sheath end and a sheath hub fixedly connected to the proximal sheath end. The dilator and sheath assembly comprises a means for providing a releasably locking engagement between the distal portion of the sheath hub and the proximal portion of the dilator hub.
The invention further comprises a releasably locking dilator and sheath assembly, wherein the dilator comprises an elongated dilator stem, a proximal dilator end and a dilator hub having a threaded portion on its distal end fixedly connected to the proximal dilator end. The sheath includes an elongated tubular portion having a proximal sheath end, a distal sheath end and a longitudinal axis extending between the proximal sheath end and the distal sheath end. The sheath further comprises two tear seams extending along the tubular portion between the proximal sheath end and the distal sheath end, wherein the two tear seams are located on opposite sides of the sheath and are coplanar with the longitudinal axis of the sheath. The sheath further comprises a first and second sheath hub portions, each of which comprise an inverted semicircular edge fixedly connected to the sheath. The first and second sheath hub portions generally encircle the tubular sheath, with spaces between the first and second sheath hub portions. The first and second sheath hub portions comprise a first and second threaded portion, respectively, at a proximal end thereof. The first and second threaded portions combined comprise a circular threaded portion forming the proximal end of the sheath which is matable with the threaded portion of the dilator hub to provide a releasably locking engagement between the dilator and the sheath.
The invention further provides a method of separating a dilator from a sheath. The method includes providing a dilator having a dilator stem extending along a longitudinal axis and a dilator hub connected to a proximal end of the dilator stem, wherein the dilator hub comprises a male threaded portion. The method also includes providing a sheath having a sheath hub comprising a female threaded portion and winged tabs having a perpendicular portion and an angular portion whereby the dilator is releasably connected to a sheath by mating the threads on the dilator hub to the threads on the sheath hub. The method further comprises rotating the dilator around the longitudinal axis in relation to the sheath, thereby unthreading the dilator and the sheath and disengaging the sheath.
The invention further comprises a method of removing a sheath from around a catheter assembly, wherein the catheter assembly and sheath are both partially disposed inside of a desired vessel to be catheterized. The sheath includes a longitudinal axis, a distal portion having a distal tip with a hollow portion aligned with the longitudinal axis of the sheath, an elongated tubular structure comprising a hollow passageway traversing the entire longitudinal axis of the sheath, a proximal portion having a proximal tip at its proximal end, a hollow passageway along the longitudinal axis of the sheath, and two opposing tear seams running the entire length of the sheath and coplanar with the longitudinal axis of the sheath. The sheath also includes a sheath hub fixedly connected to the proximal portion of the sheath. The sheath hub comprises two opposing reveals which run parallel to the longitudinal axis of the tubular sheath and are coplanar with the tear seams running along the surface of the sheath and the longitudinal axis of the sheath. The sheath hub also includes two opposing winged tabs; each tab includes a perpendicular portion and an angled portion. The perpendicular portion extends laterally from the sheath hub in a plane which is perpendicular to the plane containing the longitudinal axis of the sheath and the two opposing reveals. The angled portion of the tab extends from the perpendicular portion, wherein an angle between the proximal surface of the perpendicular portion and the angled portion is between 90xc2x0 and 179xc2x0. The method further comprises applying a distal force to the proximal surface of the angled portion of each of the winged tabs; applying a proximal force to the distal surface of each of the tabs at a point on the tab closer to the center of the sheath than the point upon which the distal force is applied to the proximal surface; and grasping the tabs of the sheath and pulling them outward from the center of the sheath, thereby separating the sheath into two halves along the tear seams running the length of the sheath; and pulling the sheath in the proximal direction.